ignore upstream url;

[shiyj]

now Dart 2.15 support to add authentication to 3rd party packages server by adding dart pub tokens add commend; if we redirect the url to https://pub.dev, the self hosted server's auth token will be taken to https://pub.dev.

this is a temporary solution before everyone update to Dart 2.15.

[MegatronKing]

This commit is helpful, thanks!